Electrical control



Jan. 10, 1939. E. MCCABE 2,143,521

` ELECTRICAL CONTROL Filed June 17, 1957 4 sheets-sheet 1 I f 5/ 35 36 s filer/4L mam 9 A. .sa s 73 78 ,739 as 72 l lo #uit H T5 5'@ n; j; a; I i f n E .x 78 46". 7,3 s 2a 6/ v 5o 79 ra 6575 4 n mnu mzrnL f- 72 68 75 78 5 .K ZY Ms 6 d sa P O 9 8 7e :E C /l 674V 2 7 7 P FI Z 6 l 7C 7/ 69 70 5*) j E INVENTOR. E /C-'Dai /Rs .MCc/as M BY A TTORNE Y.

Jan. 10,1939. l. E. MCCABE 2,143,521 L ELECTRICAL CONTROL Filed June 17, 1937 4 Sheets-Sheet 2 O ATTORNEY,

Jan. 10, 1939. l. E. MCCABE 2,143,521

ELECTRICAL CONTROL Filed June 17, 1957 4 Sheets-Sheet 3 THERMAL Ml' T61.

INVENTOR. ma e, mc cnaf BY/fgumhm A TTORNE Y.

Jan.1o,1939.Y LEMCCABE 2,143,521 ELECTRIC-AL CONTROL Filed June 17, 1937 4 Sheets-Sheet 4 MERMHL METAL l N VEN TOR. IRA E. M4' C686 l www A TTORNE Y.

l'Patented Jan. 10, 1939 UNITED STATES PATENT OFFICE V 2.14am mcrmcar, ooN'rnoL 1ra E. McCabe, Chiosco, lll.

Application June 17, 1937, Serial No. 148,856

1s calms.

Thisinvention relates to improvements in electrical controls, and more particularly to controls of this character for use with electrically operated and controlled fluid .fuel bumer mechanisms.

It is an object of this invention to construct a iluidfuei vburner control which will provide a normal predetermined period of burner operation to establish combustion and upon failure to do so cease such operation until manually restarted. It is another-object of this invention to include means to stop burner operation for a predetermined period upon a failure of combustion during a normal period of combustion as well as upon a current interruption during a normal period of burner operation, and then recycle' in an effort to reestablish combustion. It is a further object of this invention to control all recycling operations through the 'medium of a temperature device responsive to combustion conditions. It is an additional object of this invention to employ the said temperature responsive device to provide a three way operation of a main switch controlling all the electric circuits of the burner mechanism and which also acts as a recycling switch'.

With these and other objects in view referenceismade to the accompanying sheets of drawings illustrating a preferred form of this invention, with the understanding that detail changes may be made without departing from the scope thereof.

In the drawings:-

Figure 1 is a diagrammatical view of this imswitch, motor switch, relay, and electrical heating element with a wiring diagram illustrating the electrical connections of these parts as installed in a commercial form of oil burning heating system.

Figure`2 is a view in side elevation of this improved control'apparatus with the cover removed and parts broken away.

Figure 3 is a fragmentary detail view in front `45 elevation showing the operating parts in the idle position when the controlled mechanism is idle or not in operation.

FigureiisaviewsimilartoFigureSshowing 4the positions assumed by the operating parts dur- 50 ing the normal operation of the controlled mechanisxn or running podtion.

Figure 5 is a view similar to Figure 3 showing the positions assumed by the operating parts when the mainswitch has been opened by the thermal safety device.

proved control showing the main switch, ignition (ci. 15a-za) Figure 6 is an enlarged fragmentary detail view in side elevation4 of the stack operated mechanism responsive to combustion conditions, showing the parts in the idle pomtlon.

Figure 7 is a view in front elevation of Fig- 5 ure Figure 8 is a view similar to Figure 7 showing the positions of the parts in normal running position. l

In the embodiment of this invention illustrat- 10 ed, the operating parts of the control are mounted upon a panel I, preferably provided with a cover not shown. The upper portion of the panel I mounts a stack-operating mechanism responsive to .combustion conditions, similar to that disclosed in this applicants prior Patent No. 1,762,183, dated June 10, 1930, which includes an actuating shaft 2 passing through and rotatably mounted upon the panel I and operated by the expansion and contraction of a coil 3 of ther- 20 mal metal inserted in the stack of the furnace to operatev the ignition switch I, as hereinafter described and as shown in Figures 2 and 6. 'I'he bottom of panel I mounts a repulsion relay, such as disclosed in this applicants prior co-pending application Serial No. 500,747, led December 8, 1930, having a stationary primary coil P and a movable secondary coils mounted upon the core C for operating a motor switch MS. The stackoperated mechanism is mounted between the panel. I and a plate l spaced apart from the panel by posts 5. A main switch RS also used as a recycling switch and its operating mechanism is mounted between the plate l and a front Iplate 6 spaced apart from each other by posts not 35 shown. The relay and binding posts are mounted upon a plate of insulating material l spaced apart from the panel I by posts 3. v Y

Ihe stack-operated mechanism responsive to combustion conditions mounted between the panel I and the plate l, as shown in Figures 2 and 6, includes a bearing Il in plate l for the reduced end II otthe actuating shaft 2. Spaced apart from the reduced end I l the actuating shaft 2 mounts a fixed toothed disc I2 between 45 two connected, spaced-apart plates I3 and I4 having a roller Il mounted between them in engagement with the periphery of the toothed disc I2, said plates having an opening Il through which the shaft 2 passes free of engagement, 50 so the weight of the plates Il and M maintain the roller Il in engagement with the toothed disc, as fully disclosed in this spplicants said 'prior Patent No. 1,762,183, of June 10, 1930. A circularplate I1 concentric with the axis of the shaft 55 cycling main 2 ls mounted to rotate Ifreely thereon between the plate I4 and the plate 4 in spaced-apart relation to the plate i and is provided with two arcuate slots I9 and I9 concentric with said plate and equally spaced from the center thereof and each bisected by the same diameter thereof to receive two studs 20 and 2l mounted on the plate I4 and allow of a slight oscillatory movement between the plates I 4 and I1. 'I'he ignition switch I is a mercury tube switch and is mounted in a clip on a carrier bracket 22 having two depending ears 23 rotatably mounted on a shaft 1. 'I'he bracket is provided with an operator in the form of a bifurcated plate 24 secured at one end to extend upward and overlap the plate I1. The plate I1 is provided with a co-acting stud 25 which extends between the forks of the bifurcated plate 24 so that the oscillation of the plate I1 will throw the mercury tube switch I to open and close the circuit therethrough. The parts are so arranged that when the burner mechanism is idle, the ignition switch is closed.

The stack-operated mechanism responsive to combustion conditions operates upon a diieren tial in temperature so that upon an vincrease in temperature the operating shaft is caused to rotate in a counter-clockwise rdirection and upon a drop in temperature in a clockwise direction. As disclosed in' this applicants said prior Patent No. 1,762,183, the oscillation of the toothed disc I2 imparts through roller I5 a similar oscillation to the joined plates I3 and I4, and if the movement of said plates is limited, the roller I5 will ride over the teeth of the toothed disc I2 and allow further movement of the shaft 2 in either direction. To limit the oscillation of plates I3 and I4 each plate is provided with shoulders 26 and 21 in their respective peripheries equi-distant on each side of the roller I5. To limit the movement in a clockwise direction, a stud 28 is mounted on the panel I to'be engaged by the shoulder 21 and an adjustable stop isV provided to be engaged bythe shoulder 26 to limit the movement in a counter-clockwise direction. `The adjustable stop is preferably in the form of a plate 29, as shown in Figures '6 and 7, mounted to rotate upon a bearing provided therefor about the shaft 2 and is provided with an arcuate portion concentric with the'axis of the shaft with serrations 30 thereon tov co-act with a stud -3I mounted upon the panel I. The plate 29 is provided with'an angular extension 32 yterminating in a stop 33 adapted to vloe engaged by the shoulders 26 of,the plates I3 and I4.V The plate 29 adjacent the serrated portion 30 is provvided with an angular extension 39 and the portion below the serrated part is cut out from theedge, so that the serrated portionv 30 may be moved under the stud 3l by pressure upon the angular portion or handle 34 to adjust the position of the stop 33.

The vrecycling main switch RS is also a mercury tube switch and is mounted in clips upon a carrier plate 35 which is secured upon its under side to a shaft 36 mounted to rotate in bearings in the front plate 6 and panel I, which shaft passes over the disc I1 and plates I3 and I4 of -the stack-operated mechanism. Studs 31and 38 are provided upon the rear side of the front plate 6 to limit the tilting of the carrier plate 35 to the open and closed positions of the reswitch. The' recycling main switch is normally in closed position lwith plate 35 in engagement with stop 38 when the burner is idle.

In Figures 2, 3 and 4, a thermal safety device is shown in which the recycling switch RS actuating arm 39 is carried adjacent the rear side of plate 6 on one end of a sleeve 40 rotatable about a stud 4l extending between the front plate 6 and the intermediate plate 4 with the free end of the arm 39 extended and bent to engage the underside 0f the recycling switch carrier plate 35 adjacent the stop 38. The end of lthe sleeve 40 adjacent the intermediate plate 4 carries an arm 42 extending in a direction oppositerthe actuating arm 39. A counterweight 43 is mounted upon the yfree end of the arm 42 and is of sufficient mass to normally rotate the sleeve 40 to actuate arm 39 to engage the underside of the recycling switch carrier plate 35v to tilt the switch RS to the open position andcause the plate 35 to engage the stop 31, as shown in Figure 5. 'I'he arm 42 is provided with a dependingl angular latch 44, the lower free end.of which is adapted to be engaged by apin 45 to hold the actuating arm 39 against the counterweight 43 in inoperative position, as shown in Figures 1, 3 and 4, The pin 45 is carried on the free end of` a strip of thermal or bi-metallic metal 46 bent back upon itself to form an enlarged circular bend 41 having the other end secured to a portion 48 of the front plate 6. The pin 45 is adjustable in order to vary the time of the release of the latch 44 and the latch is made of thermal or bi-metallic metal to compensate for the eifect of ambient temperatures on the thermal stripl 46 whereby such temperature changes will not alter the time of release for which the pin is adjusted. The circular bend 41 is adapted to receive an electric heating element 49, the heat from which is adapted after a predetermined period following the closing of the burner circuit as determined by the position of the pin 45 `to expand the strip 46 to withdraw the pin 45 to release the latch 44 to allow the counterweight 43 toyoperate the actuating arm 39 ,to open the recycling switch RS.

To prevent operation of the safety device upon normal operation of the burner, the electric heating element 49 is made movable and is in the formaof a spool about which electric resistance wire is wrapped and is mounted on the lower free end of a carrier arm 50, the upper end'of which is pivoted upon a stud 5I extending between the intermediate plate 4 and the panel I, as shown in Figure 2. The arm 50 is provided adjacent its pivot with a branch arm 52 extending inthe direction of the disc I1. The disc-I1 is provided with arcuate extension 53 concentric therewith forming a reversely curved shoulder 54 on the side. adjacent the arm 53 and a concave shoulder -55 on the other side, as shown-in Figures 7 and 8. The free end of the branch arm 52 is provided with a roller or stud 56 extending in the path of the reversely curved shoulder 54,

and when the disc I1 is rotated in a counterclockwise direction the stud 56 is adapted to ride up the shoulder 54 to rotate the arm 50 to withdraw Athe heating element 49 from within the thermal strip 46, as shown in Figures l and A4. The arcuate extension 53 is of suicient length to maintain the heating element 49 in the withdrawn position as the disc I1 reaches the limit of its movement in that direction and remains in that position.

' The underside of the shaft 36 mounting the recycling switch carrier plate 35 above the disc I1 is provided with a toothed segment 51 to engage the periphery of the disc I1, and the l the carrier plate engaging the stop 38. Upon a counterclockwise oscillation of-the disc I1 the teeth 58 and the segment 51 mesh and impart a clockwise movement to the segment 51, but as the recycling switch is closed and the carrier plate is in engagement with the stop 38 the shaft 36of the segment 55 is reciprocated vertically within its front bearing as the teeth of the portion 58 wipe thereunder. However, when the mechanism is in the normal running position, as

Vshown in Figure 4, the teeth of both portion 58 and segment 51 are in mesh so that upon a clockwise oscillation of disc I1 a counterclockwise movement is imparted to the segment 51 and the weight of the switch RS and carrier plate 35 will continue the engagement until the carrier plate 35 is rotated to tilt the recycling switch RS to the open position and as the carrier plate approaches and engages the stop 31 the toothless concave shoulder 55 of the disc I1 will ride under the shaft segment 51 to allowfthe switch RS to return to the closed position.

'I'he stack-operated mechanism responsive to combustion conditions as constructed in accordance with this invention provides a simple means l for a three way operation ofI the recycling switch upon a change in stack temperature to control the burner circuit for recycling operations. The mechanism allows the switch RS to assume its normal closed position after a. prolonged period of decreasing temperatures when the burner mechanism becomes idle, then-closes the switch and maintains it closed during a period of rising temperatures thereafter when the burner mechanism starts operating, and opens the switch during 'a period of descending temperatures Awhen the burner flame first goes out and at the end of this period allows the switch to again assume its closed position. The stop pin 38 may be so located to permit the switch RS to assume a closed position which is not aiected by normal fluctuations in stack temperature.

'I'his mechanism represents an improvement over the conventional type of temperature operated devices responsive to combustion conditions which open and close a switch upon reverse motion of the movable member or shaft determined by a predetermined increase and decrease in temperature, or by a change in temperature, necessitating the use of complimentary switches and mechanisms to accomplish the results of this improved device wherein a switch may remain in its normal position during a continued trend in temperature in one direction, be opened if the trend changes and restored to its normal position if the latter trend persists for a predetermined number of degree change. The adjustable stop 33 may be set to increase or decrease the number of degrees drop in temperature necessary before the recycle switch RS may be closed following its opening by a fall in stack temperature. The ignition switch actuating stud 25 carried by the plate I1 is so positioned in relation to the concave shoulder 55 of the plate that it closes the ignition switch I before the switch RS closes, as the temperature falls,`

to insure, an operative -igniter before the recycling operation is begun.

The core C of the relay is mounted on the edge of the plate 8 with the primary coil P immovably mounted upon the bottom leg of the core, and the secondary coil adapted vto reciprocate thereabove about the outer leg of the core. The secondary coil S is attached to a bracket 59 pivoted to the opposite leg of the core C which bracket is extended on the side between the panel I and plate 8 to form a switch carrier plate 68 for the motor switch MS, which is also a mercury tube switch. 'I'he free end of the carrier plate G0 is provided with a flat spring extension adapted to rest upon a stud 6I mounted on the panel I when the floating secondary coil S has reached the upward end of its travel to close the motor switch MS, as shown in Figure 4. To prevent the motor switch being closed after a normal operation during which a current interruption has occurred before the heating element 49 has been returned within the thermal strip 41 and the ignition circuit restored a latch 62 is pivoted intermediate its ends upon a stud 83 mounted upon the inner side of the intermediate plate 4, as shown in Figure 2. The lower end of the latch 82 is provided with an offset arcuate interiorly serrated portion 64 adapted to normally engage a portion 65 of the motor switch carrier plate 60 extending in the path of the teeth of the part 64 when the secondary coil S rests upon the primary coil P. The upper free end of the latch 62 is provided with a stud 66 extending in the path of the heatelement carrying-arm 50 adapted to be engaged thereby when the heating element 49 is received within the thermal strip 41 to rotate the latch i 62 to withdraw the toothed portion 64 from engagement with the motor switch carrier plate 50, as shown in Figures 3 and 5, but when in normal running position the arcuate portion 64 is allowed to contact the extension 85, as shown in Figure 4, whereby upon a current interruption the secondary coil S will fall immediately causing the extension 65 to engage the teeth of the portion 64 and prevent the coil from rising or floating if the current be resumed before the heat element arm 58 operates the latch 82 to free the motor switch carrier plate.

The application of this improved vcontrol'to a commercial type of uid-fuel burner is illustrated in the diagrammatical view of Figure Lgf-The wire L from the commercial source of electricity" is connected to binding post 61 on the panel'I and by wire 88 through the recycling switch RS -to binding post 68, and when the motor switch MS is in open position,' through wire 18 through V.the windings of the primary coil Pto binding post 1I, and thence through wire'L to the commercial source. 'I'he windings of the secondary coil S are connected in circuitto thev roomv thermostat T return line L'. The ignition switch I being ,nor- 75 mally closed the current will also pass from binding post i5 through wire lt, through the ignition switch I, binding post l@ through the ignition transformer @t Vthrough wires 'lll binding posts it and 7i to the return line L', causing the electrodes E of the ignition device to ignite the fuel supplied by the operation of the motor 'l/l.

If no ignition occurs for any reason, the continued passage of the current through the heat'- ing element 139 will expand the strip le to actuate the main switch RS to open the motor circuit through arm 39 and will require a manual .re-set before operation canbe initiated, asshown in Figure 5.

If ignition occurs, the normal operation will cause the heat of combustion to operate the stack mechanism without disturbing the closed-position of the switch RS to rotate the disc il] counterclockwise, causing the shoulder 53 to rotate the heat element arm 5B, to withdraw the heating` element le from the recycling switch thermal release it and at the same time open the ignition switch I, as shown in Figures 1 and 4. When .the call for heat is satisfied, the room thermostat T opens the secondary circuit, the falling of the coil S opens the motor switch MS, and the burner mechanism operation ceases. On a fall in temperature in the stack, the stack-operated mechanism causes the disc. il to rotate in a. clockwise direction and the parts are returned to the normal idle position, as shown in Figure 3. Should the temperature fall in the stack whilethe roomv thermostat is still calling for heat, which may occur upon ame failure, the operation of the stack mechanism in following thisv trend in ternperlature will open the switch RS thus breaking the circuit through the primary coil P of the'relay and through the burner motor Burner operations then cease until a suiqcient drop in temperature results in the mechanism closing the ignition switch and thereafter the switch RS, to restart burneroperations. L'Ifcombustion occurs normal operations will continue but if .combustion fails then a shut down occurs requiringmanual re-setting.'

Upon a current interruption during normal operation, the secondary coil will immediately fall,v

and as the heat yelement arm 5@ is out of engagement with kthe latch 62, the serrated portion t@ thereof will be engaged by the extension 65 of the motor switch carrier plate, and if the current is resumed before the stack cools, the motorcannot supply fuel to the hot combustion chamber until the stack cools sumciently to returnthe parts to the idle or starting position. K

It is to be understood that, if desired, the heating element 49 may be arranged permanently within the circular bend M of the thermo or bimetallic strip 46 and the arm 50 may mount a shunt switch which will be closed upon rotation of the arm 50 to shunt the current around the heating element 49, as disclosed in this applicant's prior Patents No. 2,015,952 dated October 1, 1935 and No. 2,024,697 dated December 17, 1935w1thy out departing from'the scope of this invention.

This invention also contemplates, if desired, that in lieu of the mercury tube switch RS an open contact may be employed in which the carrier plate 51 will be thel movable member thereof and the stop 38 the fixed member. In such a 'case the post 38 and the plate 35 will be properly insulated from the other parts and connected in the circuit 68. When employing an open contact switch, the toothed segments 5l and 58 may be amaear vits operating means allowing the main switch to remain closed upon initiation of burner operation and over-ride the operating means thereafter upon an increase in temperature resulting from combustion, and causing the main switch to open and thereafter override the operating means upon a decrease in temperature resulting from a cessation of combustion, and means upon said operating means adapted after a period following cessation of combustion to allow the main switch to again close.

2. Ilhe structure of claim 1 including an ignition circuit, a normally closed ignition switch in the ignition circuit, and wherein the main switch operating means is provided with means to open the ignition switch and maintain it open during the over-ride of the main switch operating means and thereafter to close the ignition switch priorto the closing of the main switch. K

, 3. An electrically operatedl and controlled uid fuel burning mechanism, including a motor, a

vmotor switch in the motor circuit, means for operating the motor switch including a room thermostat, a normally closed main switch, electro-thermal means for opening the mainswitchI I l a predetermined .time after the closingfof the motor switch,athermally actuated device Vresponsive to combustion conditions for` opening and closing theA main switch including a movable member, a main switch operating means actuated thereby, in combination with an over-riding connectionv between the main switch'and its operating meansv allowing themain switch to remain' closedf upon initiation of burner operation 'and over-ride the operating means thereafter upon `an increase-iny temperature resulting from".

combustiomand' means upon said operating means adapted after the period following the opening of the main switch upon cessation of combustion to allow the main switch to again close, and means actuated by the main switch operating means upon establishment of combustion to prevent the opening of the main switch by the electro-thermal means.

4. The structure of claim 3 wherein the main switch is in circuit with a relay having a movable member controlling the motor switch, and wherein a latch is providedfadaptedupon a current interruption and subsequent operation of the relay member to open the switch, to hold the said member against operating to close said switch upon resumption of current until the means for rendering the electric heater inoperative restores the heater to operative condition 'and thereby actuates the latchV `to free the relay movable member.

5. The structure of claim 3 wherein the main switch is in circuit with a repulsion relay having relatively movable primary and secondary coils including means. actuated by the movement of one of said coils to close the motor switch, and

wherein a latch is provided adapted, upon a current interruption and subsequent operation of the relay to open the switch, to hold the said means against operating to close said switch upon resumption of current until the means for rendering the electric heater inoperative restores the heater to operative condition and actuates the latch to free the' relay movable member.

6. A temperature responsive operating mechanism for electric switches including a normally closed switch mounted upon an oscillating support,- an expansible and contractible member responsive to temperature changes, a member movable thereby, an operator actuated by said movable member, stops limiting the movement of the operator, aclutch allowing movement of said member beyond the limited movement of the operator, and means actuated by the operator forming an operative connection between theoperator and switch support allowing a movement of the operator in one direction without opening the switch and operating upon a movement of the operator in the opposite direction to open the'v switch, and means upon said operating means '25 upon reaching a denite position to allow said switch to assume its normal closed position, and

adjustable means to change the relative position of the stops, limiting the movement of the operator, to limit the movement of the means upon 30 the operating means from its switch closing position to determine the maximum period for said switch to remain open.

7. The structure of claim 6 wherein the switch support is normally oscillated by' the weight of 3.', the switch to close the switch, and wherein the loperative connection between .the switch support and operator includes a disc having a toothed segment with a portion thereof removed to form the means to permit thev switch to assume its 40 normal closed position.

8. The structure of claim 6 wherein the switch support is normally oscillated by the weight of 55 therewith, and wherein the axis of the said support includes a shaft mounted in a bearing' elongated vertically Vto allow the toothed segment thereon to ride over the teeth of the segment of the disc after the switch support has reached I ai)` either limit of oscillation.

10. The structure of claim 6 wherein the switch l support is providedwith means to limit itsoscillation and is normally oscillated by theweight l of the switch to close the switch, and wherein the ggperative'eonnection between the switch support and operator includes a disc having a toothed segment vand aftoothed segment upon the axis of V the oscillating switch support adapted to, mesh therewith, and wherein the axisof the said sup- 70 port includes a shaft mounted in a bearing elongated vertically to allow the toothed segment thereon to ride over the teeth of the toothed segment of the disc after the switch support has reached either limit of oscillation and cause the 7| teeth of the segments to engage and oscillate the I support to reverse the switch when moving in the opposite direction.

11. The structure of claim 6 wherein the switch support is provided with means to limit its oscillation and is normally oscillated by the weight of the switch tube to close the switch, and wherein the operative connection between the switch support'and operator includes a disc having a toothed segment and a toothed segment upon the axis of the oscillating switch support adapted to mesh therewith, and wherein the axis of the said support includes a shaft mounted in a bearing elongated vertically to allow the toothed segment thereon to ride over the teeth of the ltoothed segment of the disc after the switch support has reached either limit of oscillation and cause the teeth of the segments to engage and oscillate the support to reverse the switch when moving in the opposite direction, and wherein the' means upon said operating means allowing the switch to assume its normal closed position consists in the formation of the operator disc to .free the segment on the axis of the switch support after the teeth of the operator disc have opened the switch and maintained it open for a predetermined movement of the operator disc.

l2. 'I'he structure of claim 6 wherein the switch support is provided with means to limit its oscillation and is normally oscillated by the weight of the switch tube to close the switch, and wherein the operative connection between the switch support and operator includes a disc having a toothed segment and a toothed segment upon the axis of the oscillating switch support adapted to mesh therewith, and wherein the axis of the said support includes a shaft mounted in a bearing elongated vertically to allow the toothedseg-f ment thereon to ride over the teeth of the toothed segment of the disc 'after the switch support has reached either limitv of oscillation and `cause late the support to reverse theA switch when moving in the opposite direction and 'wherein the means upon said operating means allowingv the switch to assume its normal closed position consists in the formation of the operator disc to free the segment on the axis of the switch support after the teeth of the operator disc have opened the switch and maintained it open for a predetermined movement of the operator disc and means to adjust the relation between the two segments to adjust the predetermined movement.

13. A temperature responsive electric switch having a temperature responsive element the movement of which is adapted to actuate a switch operating mechanism including a rotatable member actuated by said element, said rotatable member provided with a toothed track, a gravity actuated operator mounting a roller adapted to travel over said track, and said gravity actuated operator acting upon said roller to hold it in contact with said track, whereby rotation of the rotatable member in either direction imparts a rotative movement to the operator, a mercury tube switch mounted upon an oscillating support, a rotatable disc mounted freely upon the rotatable member and operated by the gravity actuated operator, said disc having means forming an operative connection between the disc and switch support allowing movement of the operator in one direction without opening the switch and operating upon movement of the operator in the opposite direction to open the switch, and upon a .the teeth of the segments tolengage and oscilcontinued movement in that direction to close the switch thereafter.

14. A temperature responsive electric switch having a temperature responsive element the movement of which is adapted to actuate a switch operating mechanism including a rotatable member actuated by said element, said rotatable member provided with a toothed track, a gravity actuated operator mounting a-roller adapted to travel over said track, andv said gravity actuated operator acting upon said roller to hold it in contact with said track, whereby rotation of the rotatable member in either direction imparts a rotative vmovement to the operator, a mercury tube switch mounted upon an oscillating support, a, rotatable disc mounted freely upon the rotatable member` and operated by the gravity actuated operator, said disc having means forming an operative connection between the disc and switch support allowing movement of the operator in one direction without opening the switch and operating upon movementcf the operator in the opposite directioyl to open the switch, and upon a continued movement in that direction to close the switch thereafter, and'means for limiting the rotation of the gravity actuated operator, saidroller connection allowing further rotative movement oi the rotatable member after the movement of the operator has reached its limit.

l5. 'I'he structure of claim 1, including electrothermal means for opening the main switch a predetermined time after the closing of the moamasar tor'switch and means actuated by the main switch operating means upon establishment of combustion to prevent the opening of the main switch by the electrothermal means.

16. An electrically operated and controlled uid fuel burning mechanism, including a motor, a motor switch in the motor circuit, means for operating the motor switch including a room thermostat, a normally closed main switch connected in series with the'rnotor, a thermally actuated device resposive to combustion conditions for opening and closing themain switch including a movable member, a main switch operating means actuated thereby, in combination with an overriding connection between the main switch and its operating means allowing the main switch to remain closed upon initiation of the burner operation and override the operating meansV therefore upon an increase in temperature resulting from combustion, and causing the main switch to open and thereafter override the operating means upon a decrease in temperature resulting from a cessation of combustion, means upon said operating means acting upon reaching a denite position to allow said switch to as- 

